1. Field of the Invention
The invention relates to a method of encapsulating an article and, more specifically, to transfer molding an asymmetric encapsulation for an electronic device, and an asymmetric encapsulated electronic device.
2. Description of the Background
It is well known that electronic devices are sensitive and thus require protection from physical and environmental conditions which may degrade or completely ruin them. Therefore, it is well known in the art to protect electronic devices from these conditions by sealing them with a protective encapsulation material. This xe2x80x9cpackagingxe2x80x9d of the electronic devices protects them from the conditions which may degrade them and allows the devices to be transported and handled, and thus allows them to be easily configured with other components. Several encapsulation methods are known in the art such as under-fill encapsulation (for flip chip applications) and glob topping.
One prior-art method for encapsulating devices is the xe2x80x9ctransfer-moldingxe2x80x9d method. Transfer molding is a process through which an encapsulating material, such as a thermosetting material, is caused to flow into a cavity formed by components of a mold. The thermosetting material enters into the cavity and flows over the electronic device[s] that is[are] located within the cavity and is then xe2x80x9ccuredxe2x80x9d so that the resin hardens into a non-flowable state. Traditionally it has been important to control the flow of the material into the cavity for a number of reasons, including: to provide void-free fill over the electrical device, to control the flow of the material so as to not contaminate unwanted areas with the encapsulating material, and to control the flow of the material so as to not cause any wire displacement or other damage to the assembly.
Also, it is well known in the art to use mechanical clamping mechanisms as sealing devices in conjunction with the molding cavity to attempt to contain the thermosetting resin within the cavity prior to curing. However, because mechanical clamps must be applied in a symmetrical fashion, i.e. equal and opposite clamping forces, the configuration of the molds is limited to symmetrical designs.
Therefore there is a need for an improved encapsulation method for transfer molding electronic devices which provides a leak proof sealing mechanism for asymmetric designs while using current equipment and known materials and techniques.
In accordance with one aspect of the present invention, a method of encapsulating an article having first and second surfaces includes the following steps: positioning a first molding section in a sealing relationship with the first surface of the article; positioning a second molding section adjacent the second surface of the article; filling the first molding section thereby forcing the second surface of the article into a sealing engagement with the second molding section; and filling the second molding section. Additionally, the step of filling the first and second molding sections may include the step of filling the first and second molding sections with an encapsulating material chosen from a class consisting of epoxies (including thermo-set resins), silicones, sycar, polyimides, and polyurethanes. Also, depending on the type of encapsulating material that is chosen, an optional step of curing the encapsulating material may be required.
Another aspect of the present invention is to provide a method which includes the following steps: mounting an electrical device to a first surface of a flexible substrate such that leads from the electrical device extend to a second surface of the flexible substrate; connecting the leads to traces formed in the second surface of the flexible substrate; positioning a portion of the flexible substrate carrying the electrical device within a molding cavity defined by first and second molding sections, the substrate forming a seal with the first molding section; forming a seal between the substrate and the second molding section by filling the first molding section; and filling the second molding section.
Another aspect of the present invention is to provide a method of transfer molding, including the steps of: positioning a first portion of encapsulated material on a first surface by transfer molding; and positioning a second portion of encapsulated material, of smaller surface area than the first portion, on a second surface by transfer molding.
Another aspect of the present invention is to provide a mold, which includes: a first molding section and a second molding section. The first and second molding sections form a cavity for receiving an article to be encapsulated. The surface area of a first side of an article exposed to the cavity is greater than the surface area of a second side of the article exposed to the cavity. At least one gate for injecting encapsulating material into the cavity is provided.
Another aspect of the present invention is to provide a non-symmetrical, transfer molded, encapsulated article.
The present invention provides several advantages over prior art techniques. Yields are increased in comparison to parts which are glob topped. The method of the present invention may be carried out using existing processes and materials having well known and understood properties. Additionally, existing molding equipment may be used. Assembly throughput is increased. Those advantages and benefits, and others, will be apparent to those of ordinary skill in the art from the Description of a Preferred Embodiment, herein below.